/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.tomcat.util.http.fileupload;

import java.io.IOException;
import java.io.OutputStream;

/**
 * An output stream which triggers an event when a specified number of bytes of
 * data have been written to it. The event can be used, for example, to throw an
 * exception if a maximum has been reached, or to switch the underlying stream
 * type when the threshold is exceeded.
 * <p>
 * This class overrides all <code>OutputStream</code> methods. However, these
 * overrides ultimately call the corresponding methods in the underlying output
 * stream implementation.
 * <p>
 * NOTE: This implementation may trigger the event <em>before</em> the
 * threshold is actually reached, since it triggers when a pending write
 * operation would cause the threshold to be exceeded.
 * 
 * @author <a href="mailto:martinc@apache.org">Martin Cooper</a>
 * 
 * @version $Id: ThresholdingOutputStream.java 467222 2006-10-24 03:17:11Z markt $
 */
public abstract class ThresholdingOutputStream extends OutputStream {

	// ----------------------------------------------------------- Data members

	/**
	 * The threshold at which the event will be triggered.
	 */
	private int threshold;

	/**
	 * The number of bytes written to the output stream.
	 */
	private long written;

	/**
	 * Whether or not the configured threshold has been exceeded.
	 */
	private boolean thresholdExceeded;

	// ----------------------------------------------------------- Constructors

	/**
	 * Constructs an instance of this class which will trigger an event at the
	 * specified threshold.
	 * 
	 * @param threshold
	 *            The number of bytes at which to trigger an event.
	 */
	public ThresholdingOutputStream(int threshold) {
		this.threshold = threshold;
	}

	// --------------------------------------------------- OutputStream methods

	/**
	 * Writes the specified byte to this output stream.
	 * 
	 * @param b
	 *            The byte to be written.
	 * 
	 * @exception IOException
	 *                if an error occurs.
	 */
	public void write(int b) throws IOException {
		checkThreshold(1);
		getStream().write(b);
		written++;
	}

	/**
	 * Writes <code>b.length</code> bytes from the specified byte array to
	 * this output stream.
	 * 
	 * @param b
	 *            The array of bytes to be written.
	 * 
	 * @exception IOException
	 *                if an error occurs.
	 */
	public void write(byte b[]) throws IOException {
		checkThreshold(b.length);
		getStream().write(b);
		written += b.length;
	}

	/**
	 * Writes <code>len</code> bytes from the specified byte array starting at
	 * offset <code>off</code> to this output stream.
	 * 
	 * @param b
	 *            The byte array from which the data will be written.
	 * @param off
	 *            The start offset in the byte array.
	 * @param len
	 *            The number of bytes to write.
	 * 
	 * @exception IOException
	 *                if an error occurs.
	 */
	public void write(byte b[], int off, int len) throws IOException {
		checkThreshold(len);
		getStream().write(b, off, len);
		written += len;
	}

	/**
	 * Flushes this output stream and forces any buffered output bytes to be
	 * written out.
	 * 
	 * @exception IOException
	 *                if an error occurs.
	 */
	public void flush() throws IOException {
		getStream().flush();
	}

	/**
	 * Closes this output stream and releases any system resources associated
	 * with this stream.
	 * 
	 * @exception IOException
	 *                if an error occurs.
	 */
	public void close() throws IOException {
		try {
			flush();
		} catch (IOException ignored) {
			// ignore
		}
		getStream().close();
	}

	// --------------------------------------------------------- Public methods

	/**
	 * Returns the threshold, in bytes, at which an event will be triggered.
	 * 
	 * @return The threshold point, in bytes.
	 */
	public int getThreshold() {
		return threshold;
	}

	/**
	 * Returns the number of bytes that have been written to this output stream.
	 * 
	 * @return The number of bytes written.
	 */
	public long getByteCount() {
		return written;
	}

	/**
	 * Determines whether or not the configured threshold has been exceeded for
	 * this output stream.
	 * 
	 * @return <code>true</code> if the threshold has been reached;
	 *         <code>false</code> otherwise.
	 */
	public boolean isThresholdExceeded() {
		return (written > threshold);
	}

	// ------------------------------------------------------ Protected methods

	/**
	 * Checks to see if writing the specified number of bytes would cause the
	 * configured threshold to be exceeded. If so, triggers an event to allow a
	 * concrete implementation to take action on this.
	 * 
	 * @param count
	 *            The number of bytes about to be written to the underlying
	 *            output stream.
	 * 
	 * @exception IOException
	 *                if an error occurs.
	 */
	protected void checkThreshold(int count) throws IOException {
		if (!thresholdExceeded && (written + count > threshold)) {
			thresholdReached();
			thresholdExceeded = true;
		}
	}

	// ------------------------------------------------------- Abstract methods

	/**
	 * Returns the underlying output stream, to which the corresponding
	 * <code>OutputStream</code> methods in this class will ultimately
	 * delegate.
	 * 
	 * @return The underlying output stream.
	 * 
	 * @exception IOException
	 *                if an error occurs.
	 */
	protected abstract OutputStream getStream() throws IOException;

	/**
	 * Indicates that the configured threshold has been reached, and that a
	 * subclass should take whatever action necessary on this event. This may
	 * include changing the underlying output stream.
	 * 
	 * @exception IOException
	 *                if an error occurs.
	 */
	protected abstract void thresholdReached() throws IOException;
}
